What Is a Combi Boiler?
Around 70% of new homes in the UK now come with a combi boiler fitted, as opposed to the more traditional boilers.
So, if your home is in need of a replacement boiler, which should you choose? What is the difference between a modern (condensing) conventional boiler and a combi boiler?
Naturally, each has its pros and cons and the choice you make will come down to the needs of your household and the demands that you plan to make of your boiler.
A combi boiler gets its name from the fact that it is a combination of a very efficient water heater, as well as a central heating unit. You may think that this exactly the same as a traditional boiler, but the key difference is that a combi boiler does it all on the fly, without need of a cylinder in which to store the hot water, or a cold water tank in the loft.
Combi Boiler Pros and Cons
The lack of a hot water storage tank is both a plus and a negative for the combi boiler. It means that crucially you save the space that a hot water cylinder takes, which is helpful in new build homes, as space is at a premium.
On the other hand you lose a handy airing cupboard and, more importantly, no hot water tank means there is no emersion heater to save the day in the event of boiler failure.
If your combi boiler fails you have no hot water until you can get somebody out to fix it.
Another consideration for the combi is the demand. If you want to take a shower you will get instant hot water at mains pressure, even without having a power shower fitted.
So that’s great, but what happens when somebody else is drawing hot water in another part of the house? The answer is that the flow of hot water may be effected.
With a combi boiler it is not possible to run more than one bath or shower simultaneously. Also, if you are about to have a new combi installed you need to get your engineer to specify a combi boiler that has the right flow rate; one that is suited to your needs.
Meaning that, although all combis take their water supply directly from the mains they are not all born equally in terms of getting that water heated and out to the consumer at a rapid rate.
In general, combi boilers are a very impressive, efficient (cheaper to run), modern, space saving system, but typically they are associated with smaller, or lower occupancy homes.
Combi Boiler Checklist – The Pros and Cons.
|Feature||Conventional Boiler||Combi Boiler|
|Space Required||Needs space for cold and hot tanks (cylinder). This means using loft space and an airing cupboard.||No tanks needed, which saves space. Better for smaller properties.|
|Effiency||So long as you have a modern condensing boiler it will match the combi for efficiency.||Very efficient, as water is only heated when it is needed.|
|Cost of Installation||Two water tanks needed and cylinder. More plumbing involved.||Cheaper to install.|
|Demand||Can supply a bath and a shower simultaneously - until the stored water is all used.||Only one major water draw at a time.|
|Time to Heat Water||Around 30 minutes.||Instant hot water at any time.|
|Flow of Water||Hot water is taken from the hot water cylinder. Water is not at mains pressure, and you may feel you need to install a pump for added pressure when showering.||Hot water is delivered from the mains - and delivered at mains pressure. So Power Shower installation is probably not needed - so long as mains pressure in your area is good.|
|Improving shower flow||Can fit a power shower.||Cannot fit a power shower - but probably not needed anyway.|
|In The Event of Breakdown||Can use the immersion heater in the cylinder for hot water, but not heating.||SOS, we're cold. We have no hot water, and no heating.|
|Ease/Cost or Repairs||The system as a whole is a bit larger, but usually not much to choose between the two. Possibility of pipework to the tanks in the loft getting frozen if not well lagged.||Boiler itself is a bit more cramped and fiddly to work with, but otherwise much the same.|
|Considerations Before Purchase||Do I have the space available. How many radiators do I need and hence what size of boiler is required.||Is the mains water pressure in my area good? How many people are likely to want to bath/shower simultaneously? Do we have more than one bathroom/en suite? If so, a combi may disappoint.|
How often should your gas boiler be serviced? Find out here.